(chiefly US) The notion that one drop of white blood (i.e. any white ancestry at all) makes a person white.
2008, Laura E. Gómez, Manifest Destinies: The Making of the Mexican American Race
The silence in American public discourse about the reverse one-drop rule as it governed Mexican Americans is significant.
2015, José A. Cobas, Jorge Duany, Joe R. Feagin, How the United States Racializes Latinos
For Mexican Americans, the reverse one-drop rule operated to open up white status to Mexicans, and thereby the assumption of some political rights, but it also operated to impose a contingent whiteness.